The present invention relates to an engine analyzer apparatus used for testing internal combustion engines. In particular, the invention relates to a method and apparatus for performing cylinder misfire and power analysis of an internal combustion engine.
Engine analyzers are used to test the performance of internal combustion engines. In recent years, accuracy and reliability of engine analyzers have taken on greater importance as government engine emission restrictions have become increasingly strict. It has become increasingly important for an operator of an engine analyzer to both accurately and rapidly test the performance of internal combustion engines. In response, the automotive test industry has developed a number of tests.
A power check test is a test which indicates the relative power contribution between cylinders of an internal combustion engine. Prior to the advent of solid state ignition systems, power checks were simple but time consuming to perform. To perform a power check on an internal combustion engine using a distributor-type ignition system, a mechanic individually disconnects a spark plug wire from the distributor and watches the power drop in the engine output.
However, this prior art type of power check cannot be performed if the engine inputs and outputs are part of a closed loop engine control system, because the engine system compensates for the lost cylinder. In order to power check closed loop engine systems, a new test was developed. This test is called the fast power check. To perform a fast power check, the engine analyzer very briefly disables a cylinder while monitoring engine output. This does not give the closed loop system time to react and compensate for the lost cylinder.
A compression test is another type of engine test. A compression test is performed on an engine to indicate the compression of each cylinder. A non-invasive, relative compression test may be run by measuring voltage while cranking the engine with the starter motor. Large voltage drops in the electrical system indicate high compression, while small voltage drops indicate low compression in a cylinder. Large voltage fluctuations occur when the starter motor is heavily loaded. Thus, small voltage drops indicate poor compression. This is a non-invasive compression test which can be used to identify mechanical faults associated with each cylinder in an internal combustion engine.
Modern day internal combustion engines are often computerized and operate without a conventional distributor. This is known as a distributorless or direct ignition system. Distributorless ignition systems can be broken down into three broad classifications: DIS, direct, and DIS-direct.
A DIS-type ignition system uses one remotely-mounted ignition coil for each pair of cylinders. For example, a four-cylinder engine has two ignition coils, a six-cylinder engine has three ignition coils, and so on. In this system, one spark plug fires a positively going electric spark and the other, corresponding spark plug simultaneously fires a negatively going electric spark. Each spark plug fires once per revolution of the engine, first on a compression stroke and then on an exhaust stroke. The firing during the exhaust stroke is referred to as a waste firing. In the DIS-type ignition system, the electrical circuit through the two, spark plugs is as follows: electrical ground to a first spark plug, first spark plug to plug wire, plug wire to ignition coil, ignition coil to a second plug wire, second plug wire to a second spark plug, and second spark plug to electrical ground.
The integrated direct-type ignition system uses one directly mounted ignition coil for each cylinder. Therefore, a four-cylinder engine was four ignition coils, a six-cylinder engine has six ignition coils, and so on. In a direct-type ignition system, each spark plug typically fires a negatively going electric spark. Each ignition coil is attached to a spark plug and fires once for every two revolutions of the engine. In the direct-type ignition system, the spark plug is connected directly to the ignition coil through an adaptor.
A DIS-direct ignition system uses one directly mounted ignition coil for every two cylinders. Therefore, a four-cylinder engine has two ignition coils, and so on. In the DIS-direct ignition system, one spark plug fires a positively going electric spark and the other, corresponding spark plug simultaneously fires a negatively going electric spark. Each spark plug fires once per revolution of the engine, first on a compression stroke, and next on an exhaust stroke. The firing during the exhaust stroke is referred to as a waste firing. In the DIS-direct ignition system, each spark plug of a spark plug pair is directly connected to opposite sides of the ignition coil for that spark plug pair.
The advent of distributorless ignition systems required the development of new engine analysis equipment to test engine performance. A non-intrusive test of relative power contribution between cylinders of a distributorless ignition system-type internal combustion engine was developed. One such test is called a cylinder performance test or RPM variation test.
In an RPM variation test, capacitive probes are hooked to each spark plug wire of the engine and an inductive probe is hooked to the "No. 1" spark plug wire as a positive reference. Additionally, software means are used in some cases to guarantee correct "No. 1" synchronization. Signals from these sensors are monitored over a number of revolutions of the engine. Data is collected and stored in a computer system in the engine analyzer. After collecting the data, the times between cylinder firings are converted to revolutions per minute of the engine. Using the collected data, RPM variations between adjacent cylinders are calculated over the entire data set. The analyzer examines these RPM variations and constructs a table which shows the frequency of RPM drops at various predetermined levels of engine load.
Using this data, both major and minor faults may be located. For example, RPM variation tests can locate totally dead cylinders, as well as simple misfires.
For the cylinder performance or RPM variation test to be useful, it is necessary to have a cylinder map of the engine being tested. A cylinder map is a table which describes the firing order and location of cylinders in the engine. Additionally, the cylinder map shows how engine output is altered by a misfire. For example, a misfire in one cylinder typically does not appear as a drop in engine output until the firing of a succeeding cylinder Each new engine or engine modification must be mapped by the manufacturer of the engine analyzer equipment the map is stored in the engine analyzer. Prior to performing an engine test, an operator indicates the types, model, and year of the engine under test. Following testing, the map is applied to the test data and used to indicate the condition of individual cylinders.
It would be a useful and significant contribution to the art to perform RPM variation tests on engines without the necessity of storing individual maps for every type of engine.